People communicate wirelessly and on the go. Among the devices that make this possible are those sometimes referred to as personal mobile devices, examples of which include cell phones, smartphones, walkie-talkies, and portable hotspots, among others. A personal mobile device could be handheld, body-mounted, or vehicle-mounted, as examples.
Given the relative ease with which radio signals and other communications can be intercepted, communication with or between personal mobile devices is often encrypted to prevent successful interception of the communication by third parties. Generally speaking, encryption is the process of converting audible voice or other data into unintelligible data, while decryption is the process of converting the unintelligible data back to the original, e.g., audible voice. The respective algorithms used for encryption and decryption are often referred to collectively as a cipher. Examples of common ciphers include Advanced Encryption Standard (AES), Blowfish, Triple Data Encryption Algorithm (3DES), and RC4, among numerous others.
Although many forms of communication may be encrypted, government agencies, such as the NSA, may obtain authorization to listen in on communication sessions for various reasons, such as suspicion of criminal activity, suspicion of terrorist activity, etc.